The capillary occlusion pressure threshold is 32 mm Hg. Pressures above 32 mm Hg result in capillary closure which occludes blood flow to the tissue. Decubitus ulcers occur when the blood flow through the skin capillaries is occluded due to the compression of tissue for a prolonged period of time. Decubitus ulcers, which are also referred to as pressure ulcers, pressure sores and bedsores, are a pervasive problem in the health care field. The most crucial factors in the formation of decubitus ulcers are the intensity and duration of the pressure being applied to the area of the patient's body.
There are a variety of systems available that are intended to reduce the formation of decubitus ulcers. These systems are either static devices or dynamic devices. Static devices include foam mattresses and gel and/or air cushions and/or mattresses which attempt to redistribute support pressure away from bony prominences. For example, static air mattresses include those disclosed in U.S. Pat. No. 4,685,163 to Quillen et al., U.S. Pat. No. 5,369,828 to Graebe and U.S. Pat. No. 5,282,286 to MacLeish. Static devices are undesirable because they require frequent turning and repositioning of the patient by health care workers and do not maintain pressure relief below the 32 mm Hg capillary occlusion pressure threshold.
Dynamic devices, such as alternating air mattresses, function by alternately shifting support pressure. Generally, these devices can be divided into two general types, no air loss devices which are made of an air and liquid impervious material and are, therefore, airtight, and those which are made of materials or supplied with additional manifolds to provide for low air loss from the device.
No air loss air devices include, for example, those disclosed in U.S. Pat. No. 5,509,155 to Zigarac et al., U.S. Pat. No. 4,833,614 to Saitoh et al., U.S. Pat. No. 4,864,671 to Evans, U.S. Pat. No. 5,500,965 to Hannagan et al., U.S. Pat. No. 5,010,608 to Barnett et al., U.S. Pat. No. 5,243,721 to Teasdale, U.S. Pat. No. 4,953,247 to Hasty, U.S. Pat. No. 4,852,195 to Schulman, U.S. Pat. No. 4,796,948 to Paul et al., and U.S. Pat. No. 4,175,297 to Robbins et al. These devices, while alternately shifting support pressure are problematic due to the build up of heat and moisture at points of interface between the mattress and a patient, which leads to skin maceration and ultimately decubitus ulcer formation.
Low air loss devices, for example, are disclosed in U.S. Pat. No. 5,003,654 to Vrzalik, U.S. Pat. No. 5,267,364 to Volk, U.S. Pat. No. 5,103,518 to Gilroy et al., U.S. Pat. Nos. 5,193,237, 5,379,471 and 5,533,217 to Holdredge. Low air loss devices have been found to be particularly useful because these mattresses prevent the build up heat and moisture at points of interface between the mattress and a patient, which prevents skin maceration.
However, all of these devices have various shortcomings. For example, static devices require turning and repositioning of the patient. Alternating devices attempt to alleviate the problem of turning and repositioning by alternately inflating and deflating individual air sacks or groups of air sacks based on cyclic preselected time intervals. However, these devices, due to their alternating nature, produce areas of concentrated high pressure on the patient's body at the interface with the inflated portions and areas of little or no support on the patient's body at the deflated portions. Further, none of these devices provide a low air loss device which simultaneously prevents skin maceration due to the build up of heat and moisture at points of interface between the device and the patient, and is an active feedback system which provides for real time adjustments to the inflation pressure of the air mattress in response to an increase in the compressive pressure on a part of the mattress from shifting of the patient's weight or other causes.
Thus, what is needed then is a corrective, low air loss, dynamic patient body weight air support system which has active feedback pressure sensing and real time automatic pressure correction capabilities.
In view of the prior art as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the pertinent art how the needed dynamic patient body weight air support system could be provided. Further, it was not obvious to those of ordinary skill in the pertinent art how a dynamic patient body weight air support system having active feedback pressure sensing and real time automatic pressure correction capabilities could be provided which maintained pressures below the 32 mm Hg capillary occlusion pressure given the reduced surface area of a wheelchair seat.